Frequency bands and modes associated with various protocols are specified per industry standards for cell phone and mobile device applications, WiFi applications, WiMax applications and other wireless communication applications, and the number of specified bands and modes is increasing as the demand pushes. Laptops, tablets, personal digital assistants, cellular phones, smart phones and other mobile devices include a communication system which may be designed to have paths or chains to process signals in multiple modes and bands.
As new generations of wireless communication devices become smaller and packed with more multi-mode multi-band functions, designing new types of antennas and associated air interface circuits is becoming increasingly important. In particular, a mobile device with an air interface tends to be affected by use conditions such as the presence of a human hand, a head, a metal object or other interference-causing objects placed in the vicinity of the antenna, resulting in impedance mismatch and frequency shift at the antenna terminal. Accordingly, an impedance matching scheme is required in the device to optimize the performance by adjusting the impedance over multiple bands and modes using as little real estate as possible. Signals in different frequency bands in such a dense RF circuitry tend to interfere with each other, and in some cases even damage sensitive components if the gap between the frequency bands is small. Therefore, a proper isolation provision needs to be considered in designing such a multi-mode multi-band system having multiple paths therein. In addition to the impedance matching and isolation considerations, obtaining high linearity is important to maintain the integrity of the signal and power transfer with minimal distortion. A present-day RF communication system for mobile applications generally includes several chip-set solutions with several external components. As these parts get more and more integrated on a chip to achieve a small real estate, high speed switching and power consumption reduction, optimizations of impedance matching, isolation and linearity call for considerations of various aspects of the fabrication technology used for the integration.